Millions of people worldwide are afflicted each year with obstructive vascular disease, such as arteriosclerosis. Conventionally, stenosis of the arteries, such as the coronary arteries, has involved bypass surgery, wherein a synthetic graft or vessel harvested elsewhere in the body is exchanged for the stenosed artery.
In the last twenty years, percutaneous transluminal angioplasty (PTA) has gained wide acceptance as a less traumatic method of treating such disease. In this method, a dilatation device, typically a polyethylene balloon is disposed in the afflicted vessel, such as a coronary artery, and inflated to disrupt the plaque lining the vessel and restore patency to the vessel.
In a large number of cases, to prevent the vessel from later restenosing, a vascular prosthesis "stent") is deployed in the vessel to maintain the patency of the vessel. U.S. Pat. No. 4,739,762 to Palmaz describes one such commercially available stent, which consists of a slotted tubular member. The stent is deployed by plastically deforming the tubular member with a balloon disposed within the interior of the stent.
While use of inflatable balloons in angioplasty and to alleviate other obstructive disease have provided significant benefits to patients, some drawbacks have been recognized for such devices. For example, balloons have been observed to occasionally rupture, and may cause a life-threatening dissection of the vessel. More generally, however, an inflated balloon tends to apply a high compressive load on the endothelial cells lining the vessel. This load may result in damage to the vessel lining, and may even accelerate restenosis. Thus, it would be desirable to provide dilatation apparatus having reduced contact with the vessel lining to preserve more of the endothelium intact.
U.S. Pat. No. 5,250,070 to Parodi recognizes that conventional smooth-walled balloon dilatation devices may lead to extensive damage to the endothelial layer. That patent proposes a dilatation element comprising a series of balloon elements that form ribs when inflated, thus reducing overall contact with the vessel lining compared to smooth-walled balloons. A drawback of the device described in that patent, however, is the complex structure of the balloon member, which renders it impracticable to manufacture.
Another method of reducing contact between the dilatation member and the vessel lining involves constructing the dilatation member with a series of fixed-width bands. For example, U.S. Pat. No. 3,557,794 to Van Patten describes an arterial dilatation element comprising four flexure beams captured between two ferrules. An actuator wire runs to the proximal end of the device, and the flexure beams are made to bow outward by reducing the length of the actuator wire. U.S. Pat. No. 5,354,310 to Garnic et al. and U.S. Pat. No. 5,456,667 to Ham et al., describe devices intended for use as temporary stents to maintain the patency of a vessel for a brief period following dilatation, and which employ a wire mesh and spiral band, respectively, that are actuated by pulling a core member that extends to the proximal end of the devices.
While the dilatation and stenting elements of the aforementioned patents provide reduced contact between the vessel lining and the dilatation element, it is believed that a drawback common to these devices is the inability to transmit sufficient force to the dilatation elements by the actuator wire or core member to effectively disrupt the plaque lining the vessel. In addition, it is believed to develop very high compressive loads with such dilatation elements, the actuator wire or core members may need to be too thick t o readily negotiate tortuous vascular anatomy.
U.S. Pat. No. 4,585,000 to Hershenson describes a screw-operated expanding mandrel enclosed within an elastomeric tube. The screw arrangement in the dilatation element of the Hershenson device may develop the necessary compressive force to disrupt plaque. However, the quadrant-shaped mandrel portions and elastomeric covering employed in that device are expected to provide a compressive force similar to that encountered with smooth-walled balloons.
In view of the foregoing, it would be desirable to provide dilatation mechanisms, and methods of use, that are capable of developing the high compressive forces required to disrupt plaque resulting from obstructive disease, but which have reduced contact with the endothelium compared to smooth-walled balloon dilatation elements.
It further would be desirable to provide dilatation mechanisms and methods suitable for use in deploying vascular prostheses, but which have a lower risk of rupture.
It still further would be desirable to provide dilation mechanisms having reduced contact with the endothelium, compared to smooth-walled balloon dilatation elements, but which have an uncomplicated design and are easy to manufacture.